Early transition metal catalysts useful for olefin coordination polymerization include the traditional Ziegler-type catalysts based on Group-4-5 transition metals and the newer metallocene type catalysts based on Group-4-6 transition metals. But specific late transition metal catalysts suitable for olefin polymerization have not offered the same levels of activity or molecular weight capability for olefin polymerization. Further development of these catalyst systems has been attempted addressing these shortcomings.
Ancillary-ligand-stabilized metal complexes (e.g., organometallic complexes) are typically useful as catalysts, additives, stoichiometric reagents, monomers, solid state precursors, therapeutic reagents, and drugs. The ancillary ligand system generally comprises organic substituents that connect to and remain associated with the metal centers. These interactions provide an opportunity to modify the organometallic complexes' shape and their electronic and chemical properties.
Certain organometallic complexes are catalysts for reactions such as oxidation, reduction, hydrogenation, hydrosilation, hydrocyanation, hydroformylation, polymerization, carbonylation, isomerization, metathesis, carbon-hydrogen activation, cross-coupling, Friedel-Crafts acylation and alkylation, hydration, dimerization, trimerization, oligomerization, Diels-Alder reactions, and other transformations. Typical complex synthesis proceeds by combining an ancillary ligand precursor with a metal-containing precursor in a solvent at a temperature. For example, organometallic complexes can be single-site, olefin polymerization catalysts. Their active sites typically comprise an ancillary-ligand-stabilized, coordinatively unsaturated transition-metal-alkyl complex.
In Johnson, Killian, and Brookhart, J. Am. Chem. Soc., 1995, 117, 6414, the authors describe the use of Ni and Pd complexes for ethylene, propylene, and 1-hexene homopolymerization. The catalyst precursors are square-planar, M2+, d8, 16-electron complexes incorporating substituted, bidentate diimine ligands. Either methyl or bromide ligands occupy the active coordination sites. These polymerizations used H+(OEt2)2[B(3,5-(CF3)2C6H3)4]− to activate methyl ligand complexes and methylalumoxane (MAO) or diethyl aluminum chloride to activate bromide ligand complexes.
European Patent publication EP-A2-0 454 231 describes Group-8, -9, and -10 metal catalysts as being suitable for ethylene, α-olefin, diolefin, functionalized olefin, and alkyne polymerizations. The catalyst precursors are Group-8, -9, and -10 metal compounds that are activated by cocatalysts including discrete borate anions. This paper also illustrates ethylene homopolymerization in solutions of methylene chloride, toluene and diethyl ether. Few polymerizations were conducted in the presence of a support material, and broad molecular weight distribution polymers were produced.
WO 97/48736 describes supported late transition metal catalysts based on diimine nickel dihalide compounds where the transition metal complex was preactivated with an aluminate.
PACT publication WO 99/05154 relates to a variety of pnictide-based ligands and their uses for catalyst systems. In particular, it discloses metal compositions and compounds stabilized by an ancillary chelating ligand structure, that polymerize functionalized and non-functionalized monomers, either alone or with an activator.
Other references of interest include U.S. Pat. No. 6,586,358 B2, V. C. Gibson and S. K. Spitzmesser, Chem. Rev., 2003, 103, 283, and S. D. Ittel, L. K. Johnson, and M. Brookhart, Chem. Rev., 2000, 100, 1169.
With the discoveries of Brookhart and others, a new area of focus in polymerization catalysis now focuses on late transition metal chemistry. These types of catalyst precursors are typically nickel, cobalt or iron dihalide compounds complexed with bidentate or tridentate chelating ligands. These types of nickel catalyst precursors are typically only slightly soluble in commonplace polymerization solvents. The nickel complexes are also typically paramagnetic complexes that are difficult to characterize and purify. Depending on the oxidation state of the cobalt and iron complexes, they too can be paramagnetic. When complexes are paramagnetic, typically IR, elemental analysis and x-ray crystallography characterization is useful, however, these techniques can also be limiting. For example, for x-ray crystallography, growing crystals of fairly insoluble compounds can often be difficult. Elemental analysis requires a pure compound, again something often difficult to obtain with a poorly soluble compound because purification techniques are more limited. And while IR is a good characterization tool when used in combination with other characterization techniques, it also has its limitations—in particular, identifying and quantifying small amounts of impurities in a product. Thus, the need exists for more easily characterized and more soluble catalyst precursors that nonetheless retain or exceed the catalytic activity of prior art catalysts.